This invention relates, generally, to an antenna and a communication device including the antenna. More specifically, this invention relates to an antenna adapted to operate in more than one frequency band and a communication device including the antenna.
With the increased use of wireless communication devices, radio frequency spectrum has become scarce. In many cases, network operators providing services on one particular band have had to provide service on a separate band to accommodate its customers. For example, network operators providing service on a GSM system in a 900 MHz frequency band have had to rely on a DCS system at an 1800 MHz frequency band. Accordingly, wireless communication devices, such as cellular radio telephones, must be able to communicate at both frequencies, or even a third system, such as PCS at a 1900 MHz frequency band. Such a requirement to operate at two or more frequency bands creates a need for a wireless communication device that has an antenna adapted to receive signals on more than one frequency band.
Also, as wireless communication devices decrease in size, there is also a need to reduce the size of an antenna associated with the device. Further, while an extendible antenna offers certain advantages, such an antenna poses problems to an end user. Because the antenna will typically perform better when in the extended position, the user is required to extend the antenna before operating the wireless communication device. Many end users however prefer a fixed or xe2x80x9cstubbyxe2x80x9d antenna which do not need to be extended during operation. Accordingly, there is a need for an antenna adapted to receive signals well in multiple frequency bands without extension.
An example of such an antenna is a non-uniform helical antenna tuned to a first and a second resonant frequency as disclosed in U.S. Pat. No. 6,112,102. The non-uniform helical antenna includes a single elongated conductor that is formed into a spiral having a first section and a second section. The first section and the second section have turns of different pitches. The pitches are selected to tune the non-uniform helical antenna to the second resonant frequency. This non-uniform helical antenna suffers from a disadvantage. It is difficult to adjust the turns of the spiral to produce the different pitches.
According to an embodiment of the present invention, there is provided a helical antenna tuned to a first and a second resonant frequency. The helical antenna includes an elongated conductor formed as a uniform spiral. The uniform spiral has a plurality of turns about a longitudinal axis. The plurality of turns has a predetermined pitch and the elongated conductor has a length which is approximately one-quarter of a wavelength of the first resonant frequency. The helical antenna further includes a first dielectric element and a second element. Both the elements are coupled to the spiral to selectively tune the antenna to the second resonant frequency.
According to another embodiment of the present invention, there is provided a wireless communication device adapted to operate in at least two frequency bands. The wireless communication device includes a helical antenna as described above connected to a transceiver.